This invention relates to an x-ray film cassette and, in particular, to an x-ray cassette having a buckler and intensifying screen arrangement adapted to effect quick release of an x-ray film maintained within the cassette.
In the development of x-ray film handling systems, equipment has been provided which allows the automatic loading and unloading of x-ray film into a cassette under daylight conditions. Such equipment frees the operator from the need to load and unload a film to and from a cassette in a dark room. Exemplary of such an automatic system is that disclosed in U.S. Pat. No. Re. 28,438 (Schmidt) assigned to the assignee of the instant invention. This reissue patent describes an x-ray film package for use with a daylight loading cassette of the type disclosed in U.S. Pat. Nos. 3,784,835 and 3,870,889 (both to Schmidt and both assigned to the assignee of the present invention). U.S. Pat. No. 3,715,087 (Schmidt) describes a device used for unloading cassettes of the last-mentioned patents under daylight conditions.
In its operation, a film sheet is automatically loaded into the cassette which is operative to hold the film between two opposed substantially parallel x-ray intensifying screens during a period of patient exposure. Following exposure, the cassette is unloaded under the influence of gravity using a device, disclosed in the last-mentioned patent, adapted to release one of the two cassette plates supporting the intensifying screens to thereby relieve the holding pressure from the film sheet and allow it to drop under the influence of gravity into a light-tight container.
For a variety of reasons it is important that the time required for the film to drop from the cassette be maintained to within a reasonable maximum of no more than about six seconds. It is believed to be most advantgeous that the film drop time is of the order of three seconds or less. However, it has been found that in cassettes embodying the teachings of the above-referenced patents, the x-ray film often exhibits a tendency to adhere to one of the intensifying screens even after the holding pressure is relieved therefrom. Attempts have been made to overcome this problem through the use of cantilevered actuators (bucklers) disposed along the cassette edges which are actuated by an actuating cam assembly and pivot inwardly of the cassette to edgewise engage the film sheet and buckle the same. This creates a gap between the film sheet and the screen and permits the entry of air into the gap. The entry of air into the gap tends to equalize the pressure forces on both sides of the sheet reducing its tendency to cling to one surface or another and permitting it to respond to the influence of gravity and drop from the cassette. U.S. Pat. No. 4,383,330 discloses a cassette incorporating such bucklers.
Even with the bucklers, however, it has been found that film drop times, while greatly improved, are still sometimes unacceptably long, especially when x-ray film sheet is used with intensifying screens having an extremely smooth surface. Use of such smooth screens is desirable since it results in intimate contact between the film and the screen and consequently in improved image resolution.
Accordingly, it is believed to be advantageous to provide an x-ray cassette having a buckler assembly which will consistently and reliably operate to release the film sheet even when smooth, high resolution screens are used.